Why do many members of congress often vote as partisans?

To satisfy the members of their political party.

"the gulf of tonkin resolution in 1967".

the gulf of tonkin resolution (officially called southeast asia resolution, public law 88-408) is a law issued by the congress of the united states of america on august 7, 1964, in which president lyndon b. johnson was authorized1 to act in a comprehensive manner against the democratic republic of vietnam, which he accused of aggressions against us ships in the gulf of tonkin, where the resolution takes its name. the gulf of tonkin resolution is of historical importance because it gave authorization to the us president. lyndon b. johnson, without a formal declaration of war by congress, to use military force in southeast asia.